This investigation proposes to study the nature and significance of changes which occur in gastrointestinal motility during pregnancy and further, to explore the possibility that these changes are mediated by the sex steroids estradiol and progesterone. Digestive problems abound during pregnancy and probably reflect abnormalities at all levels of the gut; evidence strongly suggests altered motility and reduced smooth muscle contractility but definitive studies have not been done. This proposal therefore will examine small intestinal motility during pregnancy, following ovariectomy, and following treatment with sex steroids in rats chronically equipped with small intestinal electrodes. In addition, it will evaluate the myoelectric response to feeding to determine if spike activity in this setting is diminished. To better understand the significance of these changes, we also propose to study transit and growth of microoorganisms in the small intestine during pregnancy. Lastly, to evaluate the question that contractility is reduced, we will study active tension development in isolated circular muscle strips from pregnant, ovariectomized, and hormone treated animals. This investigation is being proposed because preliminary studies in rats have shown that the interdigestive myoelectric complex (IDMC), the typical fasting pattern of myoelectric activity, is sometimes absent in pregnancy. In other studies we have also shown a direct relationship between drug-induced disorganization of the IDMC and overgrowth of bacteria. Similar abnormalities in human pregnancy would thus have nutritional as well as symptomatic implications. These studies are therefore designed to provide a more fundamental understanding of altered physiology so that a logical approach to clinical problems can ultimately be developed.